Rubén Oncala Mesa

Titulation

Ph.D in High Energy Physics from the Universiteit van Amsterdam (UvA), Université Pierre et Marie Curie (UPMC - Sorbonne Université), and Universitat de Barcelona (UB).

Current Position

Research Interests

Quarks are the elementary constituents of matter, and their interactions via gluons—the carriers of the strong force— are central to understanding the behavior of matter at the most fundamental level. The strong force is unique among the four fundamental forces for exhibiting confinement at low energies, making its study particularly challenging. Traditionally, quarks were observed only in hadrons as quark-antiquark pairs (mesons, such as the pion) or in groups of three (baryons, such as protons and neutrons).

However, in the past two decades, new exotic hadrons, called XYZ states, have been discovered at particle accelerator experiments worldwide, observed in —the quark-gluon plasma—, produced briefly in high-energy heavy-ion collisions at facilities such as the LHC (CERN, Switzerland) and RHIC (USA). These states display striking and unexpected properties, and their internal structure in terms of quarks and gluons remains unclear.

My research focuses on investigating these new forms of matter. By combining quantum effective field theories with advanced computer simulations, I aim to calculate the properties of XYZ states, providing new insights into the fundamental nature of the strong force.

To understand the nature of XYZ mesons, I study both theoretical particle physics and nuclear physics, focusing on the dynamics of the strong interaction. Strongly coupled gauge theories play a central role in explaining quark and gluon confinement. My work centers on Quantum Chromodynamics (QCD) and related Effective Field Theories, with applications to:

The main tool that allows me to address such diverse problems is quantum field theory, particularly in its modern effective formulation. Much of my work has focused on non-relativistic systems and the study of heavy bound states. Investigating dark-matter bound states, charmonium and bottomonium has been crucial in my understanding of the formation of these new states of matter.

Backround

2010–2014 — Degree in Physics, University of Barcelona

I was living in Sant Boi de Llobregat, my hometown, when I started my studies in Physics at the University of Barcelona. I graduated with a specialization in High Energy Physics and began exploring the world of quarks, governed by Quantum Chromodynamics (QCD). My final degree thesis on tetraquarks is still available online.

2014–2016 — Master's in Nuclear Physics and High Energy Physics, University of Barcelona

While studying these two master's degrees, one after the other, I began working on quarkonia — bound states made of two heavy quarks. They can be studied within the non-relativistic QCD (NRQCD) framework. One possible configuration of these bound states is hybrid quarkonia, exotic hadrons with explicit gluonic degrees of freedom. As the final project for my master's thesis I published my first paper, showing how quarkonia and hybrid quarkonia are strong candidates for the XYZ mesons — a family of recently discovered particles that are still not well understood.

2016–2021 — Ph.D. in High Energy Physics, University of Amsterdam

Amsterdam period

At that time, I was excited to move to Amsterdam to begin my doctoral studies at the Dutch National Institute for Subatomic Physics (Nikhef), where I pursued my Ph.D. in High Energy Physics. There, I studied Quantum Field Theory (QFT) and Effective Field Theories (EFTs) to better understand the formation of dark-matter bound states in the early universe. During my time in Amsterdam, I also began my teaching career as an assistant lecturer for two consecutive years 2018-2020 in the course Statistical Physics — part of the second-year Physics degree program at the University of Amsterdam, where I eventually defended my Ph.D. thesis and earned my doctoral degree.

Paris period

During my contract at Nikhef, I was sent on a research mission to the Laboratoire de Physique Théorique et Hautes Énergies (LPTHE) at Sorbonne University in Paris. There, I continued exploring long-range interactions in non-relativistic systems, focusing on how such forces can lead to the formation of bound states. Working closely with researchers from both institutes gave me a broader and more unified perspective on the mechanisms that govern these systems. This collaboration also opened the door to a new line of research, where I investigated the possible connection between dark matter and ordinary matter through the Higgs portal — work that ultimately led to several publications.

2023–Present — Lecturer and Researcher at Universidad San Pablo CEU

After a period of rest, I began my current position as a Lecturer in Mathematics at Universidad San Pablo CEU. I truly enjoy teaching because it is, in essence, another way of learning. I value the time I spend with my students — not only for the human interaction but also because I learn from them. Teaching challenges me to improve continuously: to express ideas more clearly, to revisit earlier concepts I may have forgotten, and to strengthen my own understanding. I also find deep satisfaction in sharing knowledge. I believe that what we know belongs to each of us individually, but knowledge itself belongs to everyone. With this conviction, I created Tema X — a project to share my perspective on mathematics and to reveal the hidden beauty that lies behind its equations.

Teaching has proven even more powerful than I had imagined. It is the path that gives me freedom and allows me to explore what fascinates me most: the fundamental constituents of our universe — quarks and their interactions.

Publications